The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems such as plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) may be used to deposit and etch films on substrates such as semiconductor wafers. Some PEALD and PECVD systems include chandelier-type showerheads that supply precursors to a processing chamber.
The showerheads typically include a stem portion that extends into the processing chamber and a head portion connected to the stem portion. A cavity is formed behind the head portion between the head portion and an upper surface of the processing chamber. Parasitic plasma in the volume may cause unwanted deposition to occur in the volume.
There are two approaches for addressing problems associated with the volume behind the showerhead. In one approach, the volume is purged to prevent process gases from getting behind the showerhead and causing unwanted deposition. However, purging behind the showerhead does not isolate the volume. The lack of volume isolation increases the required flow rates to purge the required volume. Purging also requires high purge gas flow and some purge gas flow directionality. The higher purge gas flow tends to adversely impact process conditions by mixing with process gases and/or shifting the plasma impedance, which may cause light up behind the showerhead.
In another approach, apparatus is used to suppress the plasma in the volume to prevent unwanted deposition behind the showerhead. Plasma suppression creates a barrier over the showerhead and reduces parasitic plasma in unwanted areas of the tool.